In recent years, much research and development of magneto-optical (MO) recording media for use as high density/high capacity memory and data storage and retrieval devices has been carried out. Such media typically comprise a suitable substrate, e.g., of glass, polymer, metal, or ceramic material, coated with a perpendicularly magnetizable film used as a recording medium. Information is recorded within the medium by switching the direction of magnetization of desired portions (i.e., domains) of the perpendicularly magnetizable film. More specifically, for recording information, the recording medium is first initialized by applying to the medium a magnetic field from an externally positioned magnetic field generation device (i.e., external magnetic bias), thereby making the direction of the perpendicular magnetization uniformly upwardly or downwardly facing. A first laser beam of sufficiently high power or intensity from a suitable source, e.g., a laser diode, is then irradiated on desired recording portions of the recording medium in the presence of an externally applied magnetic bias field. As a consequence of the laser beam irradiation, the temperature of the irradiated portions (domains) of the recording medium rises, and when the temperature reaches or exceeds the Curie point of the vertically magnetizable film or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. When this state is achieved at the desired recording portions of the medium, and in the presence of the externally biased magnetic field, the direction of the perpendicular magnetization is switched, e.g., from upwardly facing (=digital logic 1 or 0) to downwardly facing (=digital logic 0 or 1, respectively) or vice versa, so as to be aligned with that of the external magnetic field. At the end of a write pulse (i.e., laser pulse), the temperature of the heated recording domain then decreases and eventually returns to room temperature by cessation of the laser beam irradiation thereof Since the alignment direction of magnetization of the recording media effected by the laser pulse heating to above the Curie temperature is maintained at the lowered temperature, desired information can thus be recorded in the magneto-optical media.
For reading the information stored in the MO media according to the above-described method, the recorded portions of the media are irradiated with a second, linearly polarized laser beam of lower power or intensity than the one used for recording, and light reflected or transmitted from the recorded portions is detected, as by a suitable detector/sensor means. The recorded information is read out by detecting the Kerr rotation angle of the polarization plane of light reflected from the recording layer or the Faraday rotation angle of the polarization plane of light transmitted through the recording layer. More particularly, since the rotation angle of the polarization plane varies depending upon the direction of magnetization of the recorded portions of the media according to the Kerr or Faraday effect, information stored within the media can be read out optically by a differential detector which decodes the polarization-modulated light beam into bits of information.
Conventional MO recording technology typically utilizes a transparent substrate and the polarized, lower intensity laser beam is transmitted through the recording medium layers for reception by the detector/sensor means for measurement of the rotation angle of the transmitted polarized light via the Faraday effect, as explained supra. However, in first surface magneto-optical (FSMO) recording systems, polarized, lower intensity laser beam light is reflected from the MO medium for measurement of the amount of rotation of the plane of the polarized laser light via the Kerr effect, again employing a suitable detector/sensor means. The FSMO type system is advantageous in that, inter alia, opaque substrate materials, e.g., polymers, can be utilized, and dual-sided media are readily fabricated. In addition, FSMO-type media can advantageously utilize such less expensive polymeric substrates with a pre-formatted servo pattern easily formed on the surface thereof by a masking and injection molding process, therefore not requiring electronic servo as in conventional hard disk drive technology.
In addition to the above-mentioned advantages, the direct irradiation of the MO layer(s) of FSMO-configured media via the front side also results in several other advantages vis-a-vis through-the-substrate illumination, e.g., FSMO systems can utilize head sliders flying over the disk surface by forming the optical and magnetic components integral with the slider, whereby the laser beam is irradiated through the slider body and directly focussed on the MO read-write layer. The recording density of MO disks, including FSMO-configured disks, depends, in major respect, on the spot size of the focussed laser beam(s) employed for writing (and reading-out) information stored in the MO medium layer(s). The minimum spot size or diameter d is limited by diffraction according to the relation d=0.5 .lambda./NA, where .lambda. is the wavelength of the laser light and NA is the numerical aperture of the objective lens of the focussing system. In MO systems utilizing conventional technology, i.e., wherein laser irradiation of the MO medium layer is through a transparent substrate, head-disk spacings are typically in the range of hundreds of microns. However, as indicated supra, first surface magneto-optical (FSMO) systems utilizing non-transparent substrates can be devised in which a flying head slider integrally incorporates the requisite optical and magnetic components. In systems of such configuration, the laser beam passes through the slider body and is directly focussed on the MO storage medium layer. Near-field optical techniques have been developed for use with such systems in order to overcome the above-mentioned diffraction limit by using a high refractive index material as a solid immersion lens ("SIL"), which SIL is positioned between the objective lens and the FSMO disk. In such systems, the laser beam spot size or diameter is determined by the aperture size of the SIL, which aperture size can be much smaller than that possible with conventional optical focussing systems.
The spacing, or air-gap, between the SIL and the FSMO disk surface is termed the "flying height" for flying-head recording. In the past, most research on FSMO systems utilizing SIL-type optics was directed towards achieving a flying height of about 5 microinches (127 nm). However, the continuing requirement for greater recording/storage density with good coupling efficiency necessitates further decrease in the flying height of such FSMO-based storage systems, such systems and media therefor being termed low glide magneto-optical ("LGMO") systems and media.
Such LGMO recording media, when fabricated in disk form for rotation about a central axis, can be adapted for use in conventional Winchester, or hard drive, devices as are employed with conventional magnetic recording media. As indicated above, hard drives typically employed for such disk-shaped media utilize flying heads for mounting transducer/sensor devices, etc., thereon, for close positioning thereof adjacent the surface of the recording media. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined small distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Therefore, as in the case of magnetic disks, a protective overcoat layer and a lubricant topcoat layer are typically applied to the disk surface for minimizing scratching and abrasion of the sensor/transducer head and the recording media surface, which can result in an undesirably high wear rate of the head and recording media surface.
However, in the case of portable LGMO recording devices, the use of a lubricating oil, e.g., a fluorocarbon-based oil, is problematic in that it is difficult to maintain the lubricating oil on the surface of the medium, thereby increasing surface scratching and wear. In addition, a FSMO-configured LGMO disk produced without lubricating oil on its surface by a given manufacturer is not necessarily compatible with similar media produced with lubricating oil by another manufacturer.
In another approach for minimizing abrasion, scratching, and wear of transducer heads, a solid lubricant is applied to the bottom surface of the flying head which comes into contact with the surface of the recording medium. However, such solid lubricant applied to the bottom surface of the flying head must have a durability many times greater than lubricant applied to the recording medium. As a consequence, application of solid lubricant only to the flying head is not sufficient for adequately reducing abrasion, scratching, and wear.
An additional difficulty encountered in the development of wear-resistant, lubricated, ultra-high recording density FSMO-configured LGMO recording media and Winchester-type drives therefor, is the above-mentioned requirement imposed by the impetus for achieving ever-higher density recording, which necessitates even further reduction in the disk-transducer/sensor spacing and mandates good coupling efficiency. The head-to-disk interface (HDI) becomes very critical as head-to-disk spacing is reduced and head fly height decreases. Conventional MO and FSMO media without a protective overcoat and lubricant layer have extremely poor tribological performance, resulting in lack of reliability of MO-based disk drives.
The above-described problems, including disk crashing during head loading, associated with the requirement for reduced head-to-disk spacing and fly height, are further exacerbated in the case of FSMO-configured LGMO media wherein the optical and magnetic components of the recording system are incorporated into the head slider.
Thus, there exists a need for reliable, high recording density single- and dual-sided FSMO-configured LGMO disks and disk-based devices including a protective overcoat/lubricant topcoat layer system, which LGMO disks allow operation with flying heads at substantially reduced flying heights and which effectively eliminate the problems and drawbacks associated with the conventional technology, i.e., scratching, abrasion, brittleness, increased wear of transducer/sensor head and recording media surfaces, and tendency for crashing during head loading, while advantageously providing good coupling efficiency.
The present invention addresses and solves the problems attendant upon the manufacture and use of high density FSMO-configured, disk-shaped LGMO recording media and hard drives, while maintaining full compatibility with all mechanical aspects of conventional disk drive technology.